Modern telecommunication power systems utilize power supplies to obtain the higher input power necessary to operate electric loads or devices utilized in conjunction with the telecommunication power systems. The electric loads can affect performance of circuits. Thus, power factor of a load is a concern in generation, transmission, distribution, and consumption of electrical power because the power factor can influence both efficiencies and expenses. For example, a power factor that is not at or near unity can increase operating costs and/or device costs (e.g., the increased current and number of hardware components needed to compensate for the non-unity power factor would drive up operating and device costs).
A power factor in an electrical load is defined as the ratio between apparent power applied to the load and actual power absorbed by the load. The power factor is related to phase displacement between current drawn by the load and voltage applied to the load. If the drawn current is in phase with, and has the same waveform as, the applied voltage, the current waveform and voltage waveform are “in phase” and the power factor is equal (or nearly equal) to unity, or “1”, and the load is resistive. When the power factor is at or near “1”, all (or substantially all) energy supplied by the power source is consumed by the load. A power factor at or near “1” provides energy efficiency advantages. For example, a power factor that is close to unity is desirable in a transmission system in order to reduce transmission losses.
When the load is reactive, the load stores energy and releases the energy during a different portion of the cycle. Such storing and releasing of energy can cause the current waveform to shift such that the current waveform is offset, or “out of phase” with, the voltage waveform. If the voltage waveform and current waveform are out of phase and/or have different waveforms, the power factor can be less than “1”. Power factors are generally stated as “leading” or “lagging”. For a leading power factor, the current waveform leads the voltage waveform. For a lagging power factor, the current waveform lags the voltage waveform.
Power factor correction is the process of adjusting characteristics of electric loads that create leading or lagging power factors. The adjustment is made in an attempt to bring the power factor at or near unity. In an example, power factor correction attempts to bring the power factor of the alternating current power circuit as close to “1” as possible and can be achieved by supplying reactive power of an opposite polarity or adding components, such as capacitors or inductors, that can operate to cancel inductive or capacitive effects of the load.
Conventional power supplies, such as power supplies rated above a certain power level, can employ a power factor correction circuit, which can cause the power factor correction (PFC) current to be in phase with the line voltage. However, conventional power supplies show a leading power factor due to electromagnetic interference (EMI) capacitors located in front of the PFC. In some instances, the power supply creates a leading power factor, which might not be suitable for use with various devices that cannot support a leading power factor, such as generators. For example, as the generator is used, the power supply that powers the load from the generator can also be creating a leading power factor. Due to the leading power factor, the generator can become out of specification and might malfunction or might need to be shut down to prevent system failures or other problems.
Further, non-linear loads can create harmonic currents that are in addition to the original or supply line alternating current. Techniques, such as filters or active power factor correction have been utilized to smooth out the current demand over each alternating current cycle in order to mitigate the generated harmonic currents. This approach however, can be difficult to implement since simple capacitors or inductors cannot cancel the harmonic circuits currents.